It is our purpose to understand how cellular systems are able to exercise genetic control over the synthesis and assembly of cellular membranes. Because disruption of the orderly process of membrane synthesis and assembly is invariably lethal, we have chosen a model system in which to conduct these studies. The facultative photoheterotrophic bacterium, Rhodobacter sphaeroides possesses the ability to synthesize and assembly an inducible membrane system, designated the intracytoplasmic membrane (ICM) in response to the removal of oxygen. Once induced, the cellular abundance and composition of this gratuitous membrane system can vary in response to incident light intensity. These added parameters of oxygen and light control of gene expression involved in ICM synthesis and assembly provide further bases for study. We have proposed to examine, at the molecular level(s) the influence of gene expression and regulation on the orderly synthesis and assembly of the major integral membrane protein complexes. We have further proposed to study specific assembly factors which are involved in the assembly of these integral membrane protein complexes, as well as their role in determination of the abundance of these complexes. Finally, we have proposed to study how oxygen and light serve to effect the presence of these integral membrane protein complexes by their regulation of gene expression involving DNA sequences both in cis and in trans to the genes under study. These studies are directly applicable to cellular membranes, their receptors and the mitochondria of human cells. Numerous diseases, malformations or metabolic imbalances are the direct result of alterations in membrane processes, especially in those activities involved in energy transduction and extracellular communications. Likewise, the role(s) of oxygen and light on human cells are well documented. How these agents serve to effect gene expression, however, is yet to be determined. In order to conduct these studies we shall employ a combination of biochemical, genetic and molecular biological approaches whereby specific genes identified to be involved in integral membrane protein complex synthesis and assembly will be studied in vitro and in situ. Further, individual components comprising various elements of the regulatory and assembly pathways will be reconstructed in vitro in order to understand the mechanisms by which they exert their biological role(s). Lastly, genetic analyses and suppressor mutations will be employed to identify interacting components comprising structural elements involved in synthesis and assembly of these membrane complexes.